The Spanish keeper was only playing because Boro’s first-choice Dimi Konstantopoulos was rested.

But he frustrated City – who returned only on Friday night from warm-weather training in Abu Dhabi – with a series of saves.

And after City substitute Frank Lampard had hit the post with an effort deflected off Adam Clayton in the 89th minute, Boro struck again in added time.

Bamford supplied the pass for substitute Kike to slot the ball home.

Karanka hailed Middlesbrough’s win at City as the best so far in his managerial career. But the Boro boss stressed he is more interested in going to Brentford on Saturday than Wembley for a FA Cup Final.

“Of course it is my best result because we have beaten one of the best squads in the world,” he said.

“And also, I’ve been a manager for only 14 months. But we also came close to winning at Liverpool in the Capital One Cup, when we lost on penalties.

“My thoughts now, though, are just on Brentford next Saturday – not possibly going to Wembley.

“Our first objective is promotion. I just want my players to enjoy today.”

PERFECT PAT-TRICK: Bamford slides in to put Boro in front [GETTY]

It was surprising that an open, cut-and-thrust tie did not produce a goal until the 53rd minute.

Boro did get the ball into the net in the 19th minute through the head of Lee Tomlin but the assistant referee’s flag had long been raised for offside.

But most of the goal threat came from City, with defender Dedryck Boyata wasting a double chance.

First, he miskicked from James Milner’s cross, then Boyata ballooned the ball over the bar at the second attempt.

David Silva – uncharacteristically – also miscued from a good position for City.

“It is my best result because we have beaten one of the best squads in the world”